Photodegradable plastics containing halogenated diphenyl ethanes

ABSTRACT

Polyolefins capable of photodegradation are prepared by incorporating in the polyolefin an additive which contains chlorine, bromine, or iodine in alpha position in an arylmethyl structure.

DESCRIPTION OF THE INVENTION

The invention relates to and has among its objects the provision ofnovel plastic compositions capable of photodegradation. Further objectsof the invention will be evident from the following description whereinparts and percentages are by weight unless otherwise specified.

Plastics have become an important part of the American way of life.Innumerable articles of manufacture are made of plastics. One of themain uses thereof is in the manufacture of containers for liquids andsolids of all kinds, particularly foods. Another important use is themanufacture of plastic sheet materials such as films and foils. Forexample, plastic films are used in agriculture for covering the soilbetween plants, thereby to prevent the growth of weeds.

One problem with plastics is that they are not easily decomposed. Thus,for example, plastic food containers thrown by the roadside do notdecompose but remain until collected, thereby polluting the environment.Similarly, plastic films used as soil coverings must be removed from thefields prior to initiating a new crop.

The invention described herein concerns a means for obviating the aboveproblems in that it provides polyolefin plastics which are capable ofphotodegradation. Containers fabricated from the plastics of theinvention when exposed to sunlight will gradually decompose andeventually crumble away. Thus, such containers when thrown along theroadside will eventually become part of the soil. Films prepared fromthe plastics of the invention when used for agricultural purposes willgradually become friable by the action of sunlight so that they can bereadily plowed into the soil.

The benefits of the invention are realized by incorporating into apolyolefin any of the compounds described below.

Group I. Phenylmethyl halides of the structure ##STR1## WHEREIN: X ischlorine, bromine, or iodine

a is 1, 2, or 3

b is 1, 2, or 3

a + b is 3 or 4

c is 4 - (a + b).

Illustrative examples of compounds included in Group I are:

α,α-dichlorotoluene

α,α-dibromotoluene

α,α-diiodotoluene

α,α,α-trichlorotoluene

α,α,α-tribromotoluene

α,α,α-triiodotoluene

Diphenyl-chloromethane

Diphenyl-bromomethane

Diphenyl-iodomethane

Diphenyl-dichloromethane

Diphenyl-dibromomethane

Diphenyl-diiodomethane

Triphenyl-chloromethane

Triphenyl-bromomethane

Triphenyl-iodomethane

Group II. Alkylphenylmethyl halides of the structure ##STR2## wherein: Xis chlorine, bromine, or iodine

Alk is an alkyl radical containing 8 to 20 carbon atoms

d is 1, 2, or 3

e is 3 - d.

Illustrative examples of compounds included in Group II are:

Alkyl (C₈ --C₂₀) phenyl-chloromethanes and the corresponding bromo andiodo compounds.

Alkyl (C₈ -C₂₀) phenyl-dichloromethanes and the corresponding dibromoand diiodo compounds.

Alkyl (C₈ -C₂₀) phenyl-trichloromethanes and the corresponding tribromoand triiodo compounds.

Group III. α-Haloxylenes of the structure: ##STR3## wherein: Each of theX's is chlorine, bromine, or iodine

d is 1, 2, or 3

e is 3 - d.

Illustrative examples of compounds included in Group III are:

α,α'-dibromo-o-xylene

α,α'-dichloro-o-xylene

α,α'-diiodo-o-xylene

α,α,α',α'-tetrabromo-o-xylene

α,α,α',α'-tetrachloro-o-xylene

α,α,α',α'-tetraiodo-o-xylene

α,α,α,α',α',α'-hexachloro-p-xylene

α,α,α,α',α',α'-hexabromo-p-xylene

α,α,α,α',α',α'-hexaiodo-p-xylene

Group IV. α-Halomethyl-naphthalenes of the structure ##STR4## wherein: Xis chlorine, bromine, or iodine

d is 1, 2, or 3

e is 3 - d

Illustrative examples of compounds in Group IV are:

1-α-chloromethylnaphthalene

1-α-bromomethylnaphthalene

1-α-iodomethylnaphthalene

2-α-chloromethylnaphthalene

2-α-bromomethylnaphthalene

2-α-iodomethylnaphthalene

1-α,α-dibromomethylnaphthalene

2-α,α-dichloromethylnaphthalene

1-α,α,α-tribromomethylnaphthalene

2-α,α,α-trichloromethylnaphthalene

Group V. α-Halo-1,2-diphenylethanes of the structure ##STR5## wherein:Each X is chlorine, bromine, or iodine

f is 1 or 2

j is 2 - f

Illustrative examples of compounds in Group V are:

1,2-dibromo-1,2-diphenylethane

1,2-dichloro-1,2-diphenylethane

1,2-diiodo-1,2-diphenylethane.

Polyolefins containing any of the above compounds (or additives as theyare often referred to herein) decompose readily when exposed tosunlight. The decomposition, however, is not instantaneous but isgradual, and the rate thereof depends on such factors as the type ofpolyolefin, the amount of the compound added, and the activity of thelatter. The reaction which takes place can be described as aphotodepolymerization in which the polymeric chains are reduced to lowermolecular weight under the influence of sunlight.

The amount of additive to be incorporated with the polyolefin depends onthe activity of the additive, and upon the desired rate ofphoto-decomposition. In general, one may use about 0.1 to 10% of theadditive, based upon the weight of polyolefin. For most purposes about 1to 5% of the additive is sufficient to obtain a reasonable and usefulrate of photo-degradation.

The polyolefin to which the invention is applied includes, for example,high and low density polyethylene, polypropylene, polybutylene,polystyrene, mixtures of polyethylene and polypropylene, vinylacetate/ethylene copolymers, and the like. The incorporation of theadditive with the polyolefin may be carried out in any of the ways knownin the art of compounding plastics. For example, intimate mixing of thepolyolefin and additive may be effected by melting and mixing thepolyolefin with the additive by any suitable means such as a mixer ofthe Banbury or Werner type or in a screw extruder. The compositions ofpolyolefin and additive can be formed into any desired articles such asfilms, tubular sheets, foils, bags, bottles, or other containers byapplication of well-known molding and fabricating techniques.

It is within the compass of the invention to use known photosensitizingcompounds such as dibenzoyl peroxide, azo-bis-isobutyronitrile, and thelike in conjunction with the additives of the invention. In someinstances such photo-sensitizers increase the activity of the additivesof the invention. Thus, polyolefins containing an additive in accordancewith the invention and a photo-sensitizer will exhibit an enhanced rateof photodegradation.

EXAMPLES

The invention is further demonstrated by the following illustrativeexamples.

Example 1 -- Photodegradable Polystyrene Films

A. Commercial polystyrene powder was first purified as follows: Thepowder (90 g.) was placed in a 2-liter Erlenmeyer flask together with510 ml. of chloroform and the mixture was shaken until dissolved. Thesolution was poured slowly with vigorous stirring into a one-gallonWaring Blendor containing 2 liters of methanol. The finely precipitatedpowder was filtered, washed with methanol, air-dried, and finally driedin a vacuum oven at 52° C. and 30 p.s.i. This procedure was repeated fora total of three times and a polystyrene containing no styrene odor wasobtained.

B. Incorporation of additive: A wide-mouth jar was charged with 3 g. ofthe purified polystyrene powder, 0.03 g. of additive, and 17 ml. ofchloroform, then shaken on a wrist-action shaker until solution wasobtained. The solution was allowed to stand for a few minutes to removeentrapped air bubbles. Afterward, the solution was spread on a 4 × 8inch glass plate with a film-casting knife with a setting of 0.038 in.The plate was suspended above chloroform in a covered tray to retardevaporation of the solvent. After the plate had dried overnight, it wasplaced in a tray containing distilled water, which floated the film awayfrom the glass. This film of polystyrene plus the incorporated additivewas about 0.004-0.005 inch thick. A piece, 3/4 inch × 13/8 inches wascut from the film and its infrared spectrum was taken.

C. Test procedure: The said piece of film was then irradiated for 66hours by maintaining it on a revolving table 9 in. in diameter with thefilm sample 6 in. from a 275-watt RS sunlamp. After irradiation, aninfrared spectrum of the sample was again determined. The extent ofphoto-oxidation was taken as a measure of the photodegradability of theirradiated material. Photooxidation was determined by measuring theincrease in the carbonyl absorption band of the irradiated sample overthat of an irradiated sample containing no additive.

D. Specific additives used: The sequence described above in parts A, B,and C was performed with the following additives, each in the amount of1, 2, 3 or 5%, based on the weight of polystyrene:

    __________________________________________________________________________    A. Diphenyl-dichloromethane                                                                           ##STR6##                                              B. Triphenyl-chloromethane                                                                            ##STR7##                                              C. Diphenyl-bromomethane                                                                              ##STR8##                                              D. Triphenyl-bromomethane                                                                             ##STR9##                                              E. α ,α,α-Trichlorotoluene                                                          ##STR10##                                             F. α,α'-Dibromo-o-xylene                                                                  ##STR11##                                             G. α,α,α',α'-Tetrabromo-o-xylene                                              ##STR12##                                             H. 1-α-Chloromethylnaphthalene                                                                  ##STR13##                                             I. α,α,α,α',α' ,α'-Hexachloro-p-xylene       4                                                                                                  ##STR14##                                             J. 1,2-Dibromo-1,2-diphenylethane                                                                     ##STR15##                                             __________________________________________________________________________

The results obtained are summarized in the following table.

                                      Table 1                                     __________________________________________________________________________                    Polystyrene plus additives                                    __________________________________________________________________________                             Amount of                                                                           Increase in                                                                           Additive                                                        additive,                                                                           carbonyl, ab-                                                                         effectiveness                          Run  Additive            %     sorbance units                                                                        ratio*                                 __________________________________________________________________________    A    Diphenyl-dichloromethane                                                                          2     0.563   2.3                                    B    Triphenyl-chloromethane                                                                           1     0.358   1.5                                    C    Diphenyl-bromomethane                                                                             2     0.997   4.1                                    D    Triphenyl-bromomethane                                                                            5     1.184   4.8                                    E    α,α,α-Trichlorotoluene                                                          5     0.521   2.1                                    F    α,α'-Dibromo-o-xylene                                                                 3     0.909   3.7                                    G    α,α,α',α'-Tetrabromo-o-xylene                                             2     0.912   3.7                                    H    1-α-Chloromethylnaphthalene                                                                 5     0.819   3.3                                    I    α,α,α,α',α',α'-Hexachloro-p-xylen         e                   5     0.773   3.1                                    J    1,2-Dibromo-1,2-diphenylethane                                                                    5     0.535   2.2                                    Control                                                                            None used           0     0.246   1.0                                    __________________________________________________________________________     *Additive effectiveness ratio is equal to the increase in carbonyl for a      particular additive divided by the increase in carbonyl obtained without      additive (control). Thus, for example, polystyrene containing                 bromodiphenylmethane is oxidized photochemically 0.997/0.246 or 4.1 times     more than polystyrene without additive.                                  

Example 2 -- Photodegradable Polyethylene Films

To 0.6 gram of powdered polyethylene resin was added a solution of 0.006gram of triphenyl-chloromethane in 0.6 ml. of acetone. The mixture wasstirred to evenly distribute the additive solution over the particles ofpolyethylene. The mixture was spread as a thin layer on a Mylar sheetsupported by a ferrotype chrome plate. After allowing the acetone toevaporate, the said layer was covered with another Mylar sheet andchrome plate. This assembly was heated for 30 seconds at 350° F. andthen pressed at 370 psi. for 30 seconds. The assembly was thentransferred to an unheated press and pressed at 4,000 psi. whilecooling. A film of polyethylene and 1% added triphenyl-chloromethanehaving a thickness of 0.003 to 0.004 inch was thus obtained.

A similar procedure was employed for the preparation of polyethylenefilms containing other additives. The temperature of the heated presswas varied from 350°-412° F., depending on the melting point of theadditive. In general, the temperature of the press was about 10° F.above the melting point of the additive.

Samples of the polyethylene-additive film and control polyethylene filmwithout any additive were tested for photodegradability as described inExample 1, except that the time of irradiation was 100 hours. Theadditives used were:

A. triphenyl-chloromethane

B. diphenyl-bromomethane

C. triphenyl-bromomethane

D. α,α,α',α'-tetrabromo-o-xylene

E. p-Dodecylbenzyl chloride

    __________________________________________________________________________    A. Triphenyl-chloromethane                                                    B. Diphenyl-bromomethane                                                      C. Triphenyl-bromomethane                                                     D. α,α,α',α'-Tetrabromo-o-xylene                      E. p-Dodecylbenzyl chloride                                                                           ##STR16##                                             F. α,α,α,α',α',α'-Hexachloro-p-xylene     G. 1,2-Dibromo-1,2-diphenylethane                                             The results are tabulated below.                                              __________________________________________________________________________

F. α,α,α,α',α',α'-hexachloro-p-xylene

G. 1,2-dibromo-1,2-diphenylethane

The results are tabulated below.

                                      Table 2                                     __________________________________________________________________________                    Polyethylene Plus Additive                                    __________________________________________________________________________                             Amount of                                                                           Increase in                                                                           Additive                                                        additive,                                                                           carbonyl, ab-                                                                         effectiveness                          Run  Additive            %     sorbance units                                                                        ratio                                  __________________________________________________________________________    A    Triphenyl-chloromethane                                                                           3     0.542   2.1                                    B    Diphenyl-bromomethane                                                                             3     0.470   1.8                                    C    Triphenyl-bromomethane                                                                            5     0.459   1.8                                    D    α,α,α',α'-Tetrabromo-o-xylene                                             5     0.781   3.0                                    E    p-Dodecylbenzyl chloride                                                                          5     0.843   3.2                                    F    α,α,α,α',α',α'-Hexachloro-p-xylen         e                   5     0.859   3.3                                    G    1,2-Dibromo-1,2-diphenylethane                                                                    5     0.474   1.8                                    Control                                                                            None used           0     0.260   1.0                                    __________________________________________________________________________

Example 3 -- Photodegradable Polypropylene Films

Polypropylene films containing additives were prepared by the sameprocedure described in Example 2. Photodegradability of the resultingfilm was determined as described in Example 1, but using an irradiationtime of 66 hours. The additives used (each in the proportion of 1%), andthe results obtained are summarized below.

                                      Table 3                                     __________________________________________________________________________               Polypropylene Plus 1% Additive                                     __________________________________________________________________________                             Increase in                                                                           Additive                                                              carbonyl, ab-                                                                         effectiveness                                Run  Additive            sorbance units                                                                        ratio                                        __________________________________________________________________________    A    Diphenyl-dichloromethane                                                                          0.879   1.7                                          B    Triphenyl-chloromethane                                                                           0.739   1.4                                          C    Diphenyl-bromomethane                                                                             0.725   1.4                                          D    Triphenyl-bromomethane                                                                            0.708   1.4                                          E    α,α,α-Trichlorotoluene                                                          0.716   1.4                                          F    α,α'-Dibromo-o-xylene                                                                 0.755   1.4                                          G    α,α,α',α'-Tetrabromo-o-xylene                                             0.725   1.4                                          H    1-α-chloromethylnaphthalene                                                                 0.685   1.3                                          I    α,α,α,α',α',α'-Hexachloro-p-xylen         e                   0.704   1.3                                          J    1,2-Dibromo-1,2-diphenylethane                                                                    0.685   1.3                                          K    p-Dodecylbenzyl chloride                                                                          0.762   1.4                                          Control                                                                            None used           0.529   1.0                                          __________________________________________________________________________

Having thus described our invention, we claim:
 1. A photodegradablecomposition comprising a polyolefin and about from 0.1 to 10% of anadditive of the structure ##STR17## wherein: Each X is chlorine,bromine, or iodine,f is 1 or 2, and j is 2 - f.
 2. The composition ofclaim 1 wherein the additive is 1,2-dibromo-1,2-diphenylethane.